Electrically actuated automatic choke



July 20, 1954 H. G. BOLTON ELECTRICALLY ACTUATED AUTOMATIC CHOKE Filed April 1 1949 Patented July 20, 1954 UNITED STATES TENT OFFICE ELECTRICALLY ACTUATED AUTOMATIC CHOKE Harry G. Bolton, Flint, Mich, assignor to Borg- Warncr Corporation, Chicago, 111., a corporation of Illinois 14 Claims. 1

This invention relates to carbureters for internal combustion engines, and more particularly to means for automatically controlling the ratio of fuel to air in such carburetors.

Heretofore, in order to obtain suitable fuel to air ratios to facilitate starting of the engine, particularly where the engine is cold, one practice has been to utilize a mechanically actuated carbureter choke control comprising a bimetallic thermostat together with a suction piston mounted in a casing secured to the carbureter body. The thermostat and piston are connected to the carburetor choke valve and control the position thereof. A stove or heater is mounted on the exhaust manifold of the associated engine and is connected by a pipe with the interior of the casing. There is a suction connection between the casing which receives the suction piston and a point in the carbureter barrel posterior to the throttle. This suction connection controls the suction piston mentioned above, and by means of a by-pass in the wall of the casing also functions to draw heated air from the stove through the casing so as to more quickly heat the thermostat, the amount of hot air drawn in being controlled in accordance with the position of the suction piston. It will be apparent that in such a system the heat transferred from the manifold through the connecting pipe is subjected to temperatures not necessarily characteristic of the manifold temperature and thereby may be rendered inaccurate as an indication of manifold temperature. To minimize this, it has been the practice to mount the carbureter and the stove relatively near to each other in order to reduce the required length of the connecting pipe. This practice, however, may result in the stove being mounted at an undesirable location on the manifold.

Furthermore, after an engine has been operating for a substantial period, and particularly during warm weather, the manifold becomes heated to a high degree and this heat is transferred to the carburetor body through the connecting pipe and the casing. Fuel in the carbureter constant level chamber is thus heated and after the engine is stopped, the temperature of the fuel in the fuel discharge passages may rise above the boiling point of the fuel. In a downdraft carbureter, the fuel caused to boil in this manner may Well bubble up through the main fuel nozzle and pass into the intake system, thereby preventing restarting of the engine until the manifold is cleaned out.

A further disadvantage of the mechanically actuated automatic choke control type carbureters is found in the difiiculty of adapting such carbureters to widely differing climatic conditions. Such adaptation may well require extensive changes in the control mechanism and since these are closely associated with the carbureter itself, service is rendered unduly expensive An object of the present invention is to provide a new and improved carbureter, and more particularly a carbureter having an electrically actuated automatic choke control.

A further object of the present invention is to provide a new and improved carbureter whereby the many disadvantages inherent in the mechanically actuated type automatic choke controls are avoided.

In accordance with one embodiment of this invention, an electrically actuated automatic choke is associated with a conventional downdraft carbureter. An electrically actuated solenoid controls the position of the choke valve in accordance with the current applied to the coil thereof and this current is controlled in accordance with the resistance of a pressure responsive resistance unit responsive to manifold pressure and a temperature responsive resistance unit responsive to manifold temperature. Since the several elements comprising the complete electrical choke need only a single electrical conductor for interconnection, each element may be placed in the most advantageous location and the undesirable effects of extraneous operating condtions are substantially avoided.

Other objects and advantages of the present invention will be apparent from the following detailed description thereof taken in conjunction with the drawings wherein:

Fig. 1 is a side elevation, partly in section, of a carbureter having an electrically actuated automatic choke control in accordance with one embodiment of this invention;

Fig. 2 is a vertical, sectional view taken substantially along the line 22 of Fig. 1;

Fig. 3 is a detail, sectional view showing a modified form of solenoid linkage for use in conjunction with the carbureter of this invention;

Fig. 4 is a detail view similar to Fig. 3 showing a modification of the solenoid control used in conjunction with the carburetor of this invention; and

Fig. 5 is a detail view showing a thermistor connected to the solenoid control.

While in the drawings a conventional type downdraft carbureter has been illustrated, it will be understood that the automatic choke mechanism of the present invention can be employed on any type of carbureter, for example, a single carbureter or a duplex carbureter, and can also be used on updraft or horizontal carbureters with equal effectiveness.

Referring now to the drawings, and particularly Figs. 1 and 2 thereof, it will be seen that a downdraft carbureter is there illustrated comprising a main body casting 16, an upper casting i l in the bore of which is disposed choke valve [2 and a lower body casting l3 in the bore of which is disposed throttle valve 15. Fuel float chamber is is located on the left side of the carbureter, as shown on Fig. 1, and a compound Venturi arrangement 57 is located in the central bore of the main body casting. In the operation of this curbureter, air enters from the upper end thereof passing down through the several sections and mixing with the fuel which is supplied to the venturi by a suitable metering jet (not shown), and the mixture is finally delivered to the intake manifold from the lower end of the body section it. In usual practice, the carbureter section [3 is bolted directly to the intak manifold of the associated engine. As the carbureter, except for the automatic choke control arrangement of this invention, is substantially conventional, no more detailed description of the structure thereof is given herein except insofar as necessary to an understanding of the operation of the automatic choke arrangement.

The electrically actuated automatic choke of this invention comprises essentially three elements. The first element is an electrically actuated solenoid 20 whereby the position of choke valve 12 is directly controlled. The second element comprises a pressure responsive unit 2| which responds to the intak manifold pressure and is mounted on the left side, as viewed in Fig. 2, of the lower carbureter section 3. The third unit is a temperature responsive unit 22 which may be mounted directly on the exhaust manifold wall 23 of the associated engine, as shown, or at some other point of the engine at which an accurate indication of engine operating temperature may be obtained. In operation, these elements are interconnected in a series electric circuit including battery 24 and therefore are interdependent in their operation.

As may be seen in Figs. 1 and 2 the choke valve 12 comprises an oval-shaped plate supported somewhat off center on a transversely disposed shaft 25, the ends of the shaft being suitably journaled in opposite sides of the wall of the upper carbureter housing section II. The choke shaft is located off center with respect to the valve disc and to the carbureter air entrance bore so that air pressure downward against the valve will tend to open the valve due to the unbalance of valve areas on either side of the shaft. Thus, when the engine is running and air is being drawn into the carbureter, there is a tendency for he valve to open. The tendency of the valve to open in response to air inlet pressure is aided by a light, coil spring 26 disposed around the left end, as viewed in Fig. 2, of the shaft 25. One end of the spring 26 is afiixed to a pin 2'! mounted in the upper housing section II and the other end of the spring 26 is fixed to lever or crank arm 28, rigidly secured to the outer left end of the shaft 25, as viewed in Fig. 2, in such manner as to apply a clockwise rotative force, as viewed in Fig. 1. As may be seen in Fig. 2, the right end of pin 2? extends into the bore of the carbureter and in this view is disposed behind the valve [2. The pin thus serves as a stop to limit the rotation of the valve to the full open position.

The tendency of the valve to open is resisted in the conventional choke arrangement by a bimetallic thermostat spring. In accordance with the present invention, the tendency of the valve 12 to open is resisted by application of current to the solenoid from the battery 24 through the elements 2! and 22. Solenoid 26 includes a bracket 30 suitably mounted on the upper section H of the carbureter housing, the bracket 3E) supporting solenoid coil 3| within which is disposed an axially movable armature 32. The left end of armature 32 is connected by link 33 to the lower, or extended portion, of lever arm 28 in such manner that when the armature 32 moves into the coil 3!, that is, moves to the right, as viewed in Fig. 1, the lever arm 23 will cause valve IE to rotate in a counterclockwise direction, thereby closing the air inlet entrance. Swivel joints 35 are located at the right and left ends, respectively, of the link 33 to permit the link to pivot slightly with respect to armature 32 and lever arm 28. The magnetic air gap at the right end of the coil 3| is closed in the embodiment illustrated in Fig. 1 by providing a soft iron core block 34, which may be a part of the mounting bracket for the solenoid assembly. The left end of core block 34 is conically indented to increase the effective exposed area. The right end of the armature 32 is correspondingly tapered to, in effect, spread out the magnetic action, that is to say, by tapering the right end of the armature it has been found possible to increase the uniformity of the action of the solenoid.

From the foregoing, it will be evident that as the coil 3! is energized, the magnetic forces attract armature 32, moving it to the right to decrease the air gap. The amount of this movement depends on the balance of forces acting on the valve [2; these forces include the air flow past the choke valve i2 and the rotative effect of the spring 26, both tending to open the valve, and the magnetic force of the solenoid coil exerted on the armature 32, tending to close the valve 12. As the current flowing through coil 3| increases, the force tending to close the valve increases, and conversely, as the current flowing through coil 3! decreases, the force tending to close the valve decreases.

As may be seen in Fig. 1, two terminal or binding posts 36 and 31 are associated with the sole noid coil 3|, the terminal 36 being connected by lead 40 to a terminal post 4| associated with the pressure responsive element 2|. The pressure sponsive element 2! comprises a housing of con ductive material having two sections 42 and 53 respectively, separated by a diaphragm 44 which is held therebetween. The two sections are clamped together by bolts 39, shown in l, and the diaphragm G4 is sealed to the right section to define with the interior thereof a diaphragm chamber 45. Right housing section 42 is threaded directly into the wall of the lower carburetor section l3, as shown in Fig. 2, and is provided with a central bore 46, the left end of which is enlarged to receive the right end of a spring 41, the left end of which spring bears against the right side of the diaphragm 4s. The right end of the bore 46 communicates with the interior of the throttle bore through a small orifice 48 formed in the left side of the wall thereof, as viewed in Fig. 2. The diaphragm 44 is, thus, spring-loaded on the right side thereof and vacuum in the throttle bore transmitted through orifice is will actuate the diaphragm against the pressure of spring 51. For any change in manifold vacuum, the diaphragm will accordingly seek a position depending upon the balance of the manifold vacuum and the preloaded spring compression. A piston or plunger 39 is located on the left side of diaphragm M and the right end of the plunger is directly connected or affixed to the center of the diaphragm. The plunger d9 has its left end ,iournaled in a cylindrical cavity 5i! formed in the left section 33 of the pressure responsive element housing. Carbon granules 5: are enclosed in the left portion of the cavity Eli and are compressed by plunger An electrode 52 connected to the terminal ll extends into the cylindrical cavity and makes electrical contact with the carbon granules the electrode 52 being electrically insulated from the body casting of the pressure responsive assembly. It will be understood that the pressure responsive assembly housing, as well as the carburetor casting, in accordance with the usual practice wherein the engine is grounded, is at ground potential.

The diaphragm chamber always maintains the same pressure as that existing in the throttle bore posterior to the throttle valve i 5, and is thus rep-- resenta'tive of the intake manifold pressure or vacuum. The space on the left side of the diaphragm i l in the diaphragm housing is maintained at atmospheric pressure through a small vent opening 53 formed in the lower side of the left housing section 43. In operation under static conditions, or when the pressures on both sides of the diaphragm 44 are equal, the pressure of spring ill transmitted through plunger 49 will give a fixed resistance in the electrical circuit from electrode 52 through the carbon granules to the body housing of the assembly. As vacuum in the throttle bore increases and is communicated through the orifice 43 to the right end side of the diaphragm, the diaphragm M will tend to move to the right, thereby reducing the effective pressure of spring ll urging plunger 49 against the carbon granules 5i, and thus increasing the resistance through the aforementioned electrical circuit. The value of the electrical resistance in this circuit will therefore vary directly with the vacuum in the throttle bore, that is, with the intake manifold vacuum.

The second terminal 37 of the solenoid coil ii is connected by lead 55 to terminal 56 of the tem perature r sponsive element 22. Temperature responsive element 22 comprises a cup-shaped housing 5'? which is secured to the exhaust manifold wall 23 by bolts 60 and may be as shown of electrically non-conductive material, or be otherwise suitably insulated from the exhaust manifold. perature responsive unit may be located on the engine block or at any other suitable point on or associated with the engine which will provide an accurate indication of engine operating temperature. The temperature responsive resistance itself comprises a flat coil 6% of a suitable electrical conductor which is located within the housing 5? and electrically insulated from the exhaust manifold by the thin sheet 62 which may be made of any suitable non-conducting material which will not deteriorate at the temperatures to which it would be exposed in this location. While it is necessary to insulate the coil 5! electrically, the sheet 62 must be thin enough so as to avoid affect-- ing the response of the coil to changes in oper- It will be understood that the temating temperature. One end of the coil 6! is connected to binding post 56, while the opposite end is connected to a second binding post 33 mounted on the housing 5! adjacent terminal 5t. Binding post 63 is normally connected through the engine ignition switch, indicated schematically at as, to the ungrounded side of the battery 24. Since the resistance of most electrical conductors varies directly with absolute tempera ture, an increase in the temperature of the coil 6| caused by heat conducted to it through the wall of the manifold, will cause the resistance of the coil to increase.

From the foregoing it will be evident that when the ignition switch 64 is closed with the engine cold, the electrical resistance presented in the series circuit by the pressure responsive unit and by the temperature responsive unit will be a minimum, and, therefore, the maximum current will flow through the solenoid coil 3!. This, in turn, will exert maximum force tending to close the choke valve l2. As the engine starts, the vacuum in the throttle bore will increase, there by increasing the electrical resistance of the pressure responsive unit and proportionately reducing the ilow of current through the solenoid coil in accordance with the vacuum in the intake manifold. This, in turn, will decrease the magnetic force tending to maintain the choke valve in closed position. The action of the pres* sure responsive unit is very rapid, and therefore the forces on the choke valve will rapidly follow differences in manifold vacuum, a highly desira ble feature. As the engine becomes Warm, in the course of operation, the temperature responsive coil 6| will increase in electrical resistance, thereby further decreasing the flow of current through solenoid coil 3|. This will act in the same manner as the pressure responsive element to control the operation of the solenoid, except that the temperature response will be somewhat slower and have less rapid fluctuation since it follows the heat pattern of the engine itself.

A modification of the solenoid assembly is illus trated in Fig. 3 wherein the coil spring 65 has been substituted for the link 33 and swivels 35. The spring 65 provides a somewhat softer action and may be desirable to give more flexibility to the device.

In Fig. 4 the core block 34 has been omitted from the right end of the solenoid coil. This produces a different type of magnetic air gap or path and has a tendency to modify the solenoid action in that it reduces the harshness of operation. This modification may be, of course. employed in conjunction with the spring 65.

In Fig. 5 a further modification is illustrated wherein in place of the temperature responsive unit 22, a resistance 66 having a negative temperature coeflicient is utilized, the resistance 86 being connected in parallel or shunt with the terminals 36 and 31 of the solenoid coil 3!. Resistances having a high negative temperature coeiiicient of resistance, and made of a class of materials known as semiconductors, that is materials whose conductivity lies between that of conductors and insulators are sometimes referred to as thermistors and are manufactured and sold by the Western Electric Company, New York, N. Y. These types of resistances respond very rapidly to temperature changes, having a very low mass in themselves. Such an element, therefore, is particularly adaptableto the use indi cated in conjunction with the present invention. The resistance 66 is mounted at any convenient point on the engine, in a manner similar to that used for the temperature responsive unit 22. While a resistance 66 has been shown in con 'unction with the type of solenoid shown in Fig. 1, it will be understood that it is equally applicable to solenoids of the type shown in Figs. 3 and 4.

In order to reduce drain on the electrical system of the engine with which this automatic choke is operated, a normally closed thermal switch 61 may be connected in series in the line G0, as shown, or equally well in the line 55. Such a switch would constitute a temperature responsive circuit breaker which would open the electrical circuit when a certain designated operating temperature of the engine was reached. When the operating temperature drops below a predetermined point, then the switch closes and the automatic choke of this invention again becomes operative. Like the temperature responsive element 22, the switch 61 may be located at any convenient and suitable point on the engine.

Where herein the various parts of this invention have been referred to as being located in a right or a left position or in an upper or a lower position, it will be understood that this is done solely for the purpose of facilitating description and that the references relate only to the relative positions of the parts as shown in the accompanying drawings. It will be understood that each electrical unit in the control circuit may be shifted in its relation with the other circuits without changing the operation of the circuit as a whole.

What is claimed is:

1. A choke for a carbureter comprising electrically actuated means for controlling said choke, means for applying energizing current to said choke controlling means, temperature responsive means for modifying continuously throughout a substantial range the current applied to said choke controlling means from said energizing means, and pressure responsive means for modifying the current applied to said choke controlling means from said energizing means.

2. A choke for a carbureter including electrically actuated means for controlling said choke continuously throughout a substantial range, and an operating circuit for said electrically actuated means including pressure responsive resistance means arranged to respond to a selected engine operating pressure condition.

A choke in accordance with claim 2 wherein the pressure responsive means comprises a plurality of carbon granules, a piston for compressing the granules, and a diaphragm for controlling the operation of the piston.

4. In an automatic choke, a choke valve, a solenoid connected to said valve for moving said valve to closed position, current supply means connected to said solenoid for energizing the solenoid, and a resistance device the resistance of which varies with pressure connected to said current supply means and said solenoid and adapted to be associated with the intake manifold of an engine and to respond to the pressure therein to modify the current supplied to said solenoid.

5. A carbureter including means effective to vary the ratio of air to fuel in accordance with variations in intake manifold pressure, comprising a choke, electrically actuated means for closing said choke, and an operating circuit for said electrically actuated means including a resistance, the value of which varies continuously in accordance with intake manifold pressure.

6. A carbureter including a choke valve for controlling the flow of air into said carbureter, a shaft for supporting said choke valve in said carbureter, crank means disposed at one end of said shaft and keyed thereto, a solenoid associated with said carbureter, an armature connected to said crank means so that movement oi the armature causes rotative movement of the shaft supporting the choke valve, and an operating circuit for said solenoid including pressure responsive resistance means and temperature responsive resistance means.

7. A carbureter in accordance with claim 6, including resilient means connecting said armature to said crank means.

8. A choke for a carbureter comprising electrically actuated means for varying continuously the effectiveness of said choke throughout a substantial range, and an operating circuit for controlling said electrically actuated means including a thermo-responsive switch for opening said operating circuit at a predetermined temperature level.

9. A choke system for an engine carburetor comprising continuously effective means for urging the choke towards open position, electrically actuated means for continuously urging the choke toward closed position, current supply means connected to said electrically actuated means, control means responsive to selected engine operating condition for continuously controlling throughout a predetermined range the current supplied from said supply means to said electrically actuated means, and means responsive to a selected engine operating condition for disconnecting said supply means from said electrically actuated means.

10. A choke for an engine carburetor including a spring for urging the choke toward open position, electrically actuated means for urging said choke toward closed position, an electrical con trol circuit including a resistance, the value of which is arranged to vary continuously throughout a substantial range according to the engine operating conditions, a current source connected to said electrically actuated means for energizing the same, and means independent of said resistance and responsive to a selected engine operating condition for disconnecting said current source.

11. A choke arrangement for an engine carburetor including a choke valve, a solenoid for moving said valve toward choking position, means continuously urging said valve toward open position, a control circuit for said solenoid for energizing said solenoid and continuously controlling said choke valve throughout a substantial range in accordance with the varying engine operating conditions, and means responsive to a selected engine operating condition for disconnecting said control circuit for said solenoid.

12. A carburetor for a motor including means effective to vary the ratio of air to fuel in accordance with variations in intake manifold pressure, comprising a choke, electrically actuated means for closing said choke, an operating circuit for said electrically actuated means including a resistance, the value of which varies continuously in accordance with intake manifold pressure, and a thermo-responsive switch for disconnecting said operating circuit from said means upon the motor reaching a predetermined temperature value.

13. A choke for a carbureter including an electrically actuated means and a pressure responsive means for controlling said choke continuous1y throughout a substantial range, and. an operating circuit for said eiectrically actuated means including a source or" electrical supply and a thermo-responsive means, said thermo-responsalve being arranged to respond to a se lected engine temperature for disconnecting said electrically actuateo. means from said source of supply.

14. A choke for a carbureter comprising an electrically actuated means and a pressu e responsive means for controlling the effecti' eness of said choke throughout a substantia1 range according to engine operating conditions, and an operative circuit connecting said electrically actuated means with a source of supply inciuriing thermc-responsive switch arranged to disconnect said source of supply from said electrically actuated means at a predetermined engine temperature.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,577,786 Sisson Mar. 23, 1926 1502155 Brctz Nov. 2, 1926 1,913,131 Sisson June 6, 1933 2,03%,911 Moore Apr. 21, 1936 2,621,633 Hunt Feb. 23, 1937 2,158,424 Hunt May 16, 1939 2,209,218 Antcnidis July 23, 1940 2,309,41 Sisson Jan. 26, 1943 2,481,259 Taylor Sept. 6, 1949 

